Telex Communications, Inc.

Marvin M Gehr

Howell D Pabian

To reduce noise-ups, a radio receiver includes a comparator which is electrically connected to a variable potential to set a threshold voltage and connected to the IF circuit of the radio for comparison. The output of the comparator is applied to voltage controlled resistance circuits so that as the strength of the signal drops below the threshold value, the resistances are reduced. These reduced resistances are in shunt with a filter resistor so that as the resistance drops, the frequency response of the filter is lowered. Signals from the IF stage are passed through the filter before being transmitted to the audio stage so that as the signal strength drops below the threshold value but before a complete dropout, the frequency response is lowered.

Noise suppression circuit

To reduce fading in a diversity receiver, the signals received on two spaced-apart antennas are added together without phase shift while amplitude of the sum is above a certain threshold. When the signal falls below the threshold, the signal from a squelch detector causes the sum amplitude to be stored and then a 180.degree. time delay to be inserted between one of the antennas and the adding circuit, after which time, the new sum amplitude is compared with the stored signal amplitude. If the new signal has increased or remained the same, the 180.degree. phase shift remains in place but, if it has deteriorated, it is removed and the circuit reset.

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Lincoln, NE, United States of America

Marvin M Gehr